throttled for using too much *speed*

Throttled for using too much speed. Not data. Speed.

New to this sub. If this has been discussed here already, I'm sorry. I did a search but didn't find any related posts, so I figured I'd go ahead and ask you guys about this.

Have Internet 12. Yesterday wifi suddenly slowed to less than a crawl, and can't connect more than one device at a time. Devices connected to the gateway by ethernet cable are fine -- getting 12-16 Mbps.

Called AT&T to report that my wireless access point is failing. The agent checked my account and then told me that the access point is fine, and actually AT&T has slowed me down because the things I've been doing this month have used download speeds that have averaged greater than 12 Mbps. So now I'm being throttled until the next billing period.

Note that I'm nowhere near my monthly data limit.

Anyone else encountered this? Did I miss some fine print? I've never heard of anything like this. I'd expect that they'd limit me to 12 Mbps, and that would be the end of it. But the agent claimed that instead they keep track of my average speed, and if it's too high, then they throttle me way down to keep my average under 12 Mbps over the life of the current billing period. This seems crazy. How would I even know what my average speed is? There's no way to view that metric.

Also, anyone had their wifi specifically targeted for throttling? I didn't even know that was possible.

Edit: Called back and got a different agent. They're sending a tech out in the morning. Apparently the first agent was bullshitting just to try to get me to upgrade my plan. Ridiculous. Sorry about this stupid post.